Ionizing-type fire alarm sensor

ABSTRACT

A housing structure, made of metal, includes at least three interlocking parts, having interengaging elements which operate in different directions, in space, for example elements 1 and 2 being connectable by rotation in one direction, elements 2 and 3 being connectable by vertical movement and, if desired, rotation in another direction to permit ready disassembly of selected elements for cleaning and maintenance without, however, accidental dislodgment of the elements of the structure in case of fire or exposure to high temperature. The first part forms a socket; the second part includes an electric circuit and one portion of an ionization chamber with a radioactive substance; and the third part forms the other portion of the ionization chamber, containing no radioactive substances and shielding the second part from dust and dirt.

" 22 Filed:

Unite States atent 1 1 Lampart et al.

[ Oct; 23, 1973 1 IONlZlNG-TYPE FIRE ALARM SENSOR [75] inventors: ThomasLampart, Mannedorf; Max Kuhn, Stafa, both'of Switzerland [73] Assignee:Cerberus AG., Mannedorf,

Switzerland July 15, 1971 {21 Appl. No.: 162,781

I 30] Foreign Application Priority Data July 23, 1970 Switzerland11203170 [52] [1.8. Ci. 250/83.6 FT, 250/43.5.D, 250/44, 313/54, 340/237S dirt.

Primary ExaminerArchie R. Borchelt Attorney-Robert D. Flynn et a1.

[57] ABSTRACT A housing structure, made of metal, includes at leastthree interlocking parts, having interengaging elements which operate indifferent directions, in space, for example elements I and 2 beingconnectable by rotation in one direction, elements 2 and 3 beingconnectable by vertical movement and, if desired, rotation in anotherdirection to permit ready disassembly of selected elements for cleaningand maintenance without, however, accidental dislodgment of the elementsof the structure in case of fire or exposure to high temperature. Thefirst part forms a socket; the second part includes an electric circuitand one portion of an ionization chamber with a radioactive substance;and the third part forms the other portion of the ionization chamber,containing no radioactive substances andshielding the second part fromdust and 13 Claims, 2 Drawing Figures 1 IbNIZlNG-TYPE FIRE ALARM SENSORThe'present invention relates to ionizing-type fire alarm sensor, andmore particularly to a structure in which at least one radioactivesubstance is included within the sensor located within an ionizationchamber accessible to outside atmosphere; and which further includes anelectrical circuit to generate and transmit an electrical'alarm signal.

Ionizing-type fire alarm sensors, for use in fire alarm systems includea measuring-chamber'in which atmosphere is ionized by a radioactivesubstance localized therein. An ion current will be'obtainablevbetweenelectrodes located in the ionization chamber. lf smoke, smoke aerosols,or other particles penetrate through openings into the ionizationchamber, then the electrical ionization current will change and thischange in current can be utilized to provide an'alarm signal, forexample to a central fire station. The electrical circuits are as closeto the ionization chamber as possible and are in circuit with aresistance element, for example a second reference ionization chamberbeing completely,

or practically completely closed off against smoke aerosols, smoke orthe like. The potential difference between two chambers is thendetermined by means of a high resistance amplifierv element, for examplea field effect transistor (FET). The charge on the electrodes in theionization chamber can also be determined, from 1 time to time, forexample by scanning in order to detertion, dirt, and otherinterfering'effects' which decrease i the insulation resista'nce.Additionally, particles in the immediate. vicinity of the sensor, suchas dust, are also ionized andtransported within the measuring chamber,to be deposited therein. Smoke aerosols are likewise deposited Thus, thefire alarm sensors have 'to be cleaned-frequent ly' and, particularly,the ionization chamberrequires cleaning. Such cleaningand mainte fianceis time-consuming,{frequently difficult and sometimes dangerous.

necessary to carry, out the maintenance and cleaning work.

7 If a fire should start, the increase in temperature can melt plasticparticles located within the socket and the ionization sensor. Someconstructions have been made in which the entire sensor, or at leastparts thereof containing the radioactive source may fall off, thuscausing radioactive contamination of the fire location.

It is an object of the present invention to provide an ionization-typefire alarm sensor which can be interchanged rapidly and simply, whichcan be checked and cleaned by essentially. unskilled personnel withoutcausing any hazards to the personnel or subjecting the p'ersonnelfltobe' exposed to radiation, and which is so constructed that thesensoritself cannot be.damaged by accidental contact with its circuitcomponent. Additionally, the construction should be such thatradioactive substances cannot be released from the sensor even ifplastic particles therein should melt.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the ionization sensorcomprises a housing structure having at least three interlocked partswhich are formed with engaging, independently separately interlock meansto enable individualseparation of the parts from each other. One of theparts forms a socket and is adapted to be secured to a supportsurface,;such as a ceiling.-It has electrical contacts and is adaptedfor connection to an electrical alarm system. A second'part has.separable contacts engaging with the contacts on the first,ceiling-mounted part and is shaped to form one portion of an ionizationchamber within which radioactive substances can be maintained.Electrical circuit components are located on an insulating board ofthe'second part, for example bybeing placed ona printed circuit A thirdpart is then provided; comprising the other portion of'the' ionizationchamberhaving' no radioactive substances, independently separable fromthe other parts which surrounds at'least 'the sec- 0nd part and isshaped'to form a'dustand atmosphere The sensors are usually constructedas compact,

plug Jn units which can be plugged-into a mounting surdistributionshield for the second part. The interengaging interlocking means ares'oarranged that, between a first pair of adjacent parts, separation can beeffected by motion in a predetermined direction, for example clockwiserotation; and the interlocking means between one of the'parts of thefirst pair and the remaining part is so arranged as to be separable uponmotion in a different direction, for example longitudinally,

which may, if desired, be coupled with a rotary motion consuming:additionally, the sensors have to be recuit, for example the fieldeffect transistor at the input,

as well, in the form ofa bayonet latch.

The construction infaccordance with this concept permits separation ofthe third part, which forms, together with a'portion of the second part,the ionization chamber to be separately removed and-cleaned: theconstruction is preferably so selected thatall surfaces subject tocontamination by dustor dirt'are separated upon removal of the thirdpart, the ionizing element itself being shielded from suchcontamination. The sec 0nd part, together with the radioactive substanceand the electrical circuit which is sensitive to touch can remain in thesocket. If desired, the second and third 'part can'be removed together,or the second part can beremoved separately after removal of the third.Screw connections, for example by set screws can be provided to preventseparation of the second part containing the ionizable substance so thatthis portion can be removed only by trained personnel under appropriatesafety regulations. v

Separable, independent interlocking interconnections are arrangements inwhich one or both parts have spring elements which are pressed fromtheir rest or normal position and which then can snap into holes,notches, grooves or recesses in order to retain the parts together, ifand only if they are in the proper locking position. The springelements, at least in part, are accessible from the outside, withorwithout any separate tools, so that they can be pressed from theirrest position in order to release the interconnecting parts. Snapsprings, spring rings, bayonet connections or other arrangements withsimilar function are suitable.

in a preferred form, the interlocking connections are so made that theycan be reached from ground level directly, or by means of a simpleseparating tool which can be raised to the ceiling. If the springyelements are movable in different directions, then, by selecting thedirection of movement, only the third part or the second and third parttogether can be, selectively, removed.

The invention will be described by way of example with reference to theaccompanying drawings, wherein:

FIG. 1 is a vertical sectional view of the three portions of theionization sensing device, in exploded, removed form; and

FIG. 2 is a generally perspective view of a similar ionization-typesensor, partly cut open, with the second and third part connected andthe second part removed from the first; and illustrating further aremoval tool, in schematic form, aligned in engagement with the sensor.

The socket, which forms one part of the separable ionization sensor is acylindrical housing 1 having a base 2 which can be secured to a supportsurface, for example a ceiling. This housing, preferably, is of metal.The housing is formed at various portions of its circumference withslits 3; the material punched out from the slits is bent inwardly as aninwardly projecting angle 4. A part 5, for example of plastic orceramic, is secured to the bottom shell 2 of the housing. Part 5 carriesat its bottom side a plurality of contact springs 6 which are readilymovable in vertical direction. The contact springs 6 are connected withelectric connection wires 7 which interconnect the various sensors amongeach other, and with a fire alarm central station. The contact springs 6additionally form the connection between these lines and matchingsuitably arranged contact surfaces 8 on the second part of the sensor.An outer shell 9 which may consist, for example, of plastic can be usedto adapt the sensor to various types of attachments, for example to firealarm outlet boxes or the like.

The second portion of the fire alarm sensor includes a ring 10 ofinsulating material, for example plastic, and having suitably shapedgrooves and projections. A plate 11 of insulating material is secured toring 10. The upper part of plate 11 has a printed circuit placedthereon. The circumference of plate 11 is formed with various slits 12through which the inwardly extending angles 4 can pass. By relativerotation of the second part with respect to the first, the angle 4 willslide over camming element 13, formed, for example, as a projectingpunchmark, and lock in position by means of pressure of spring 6 on theinsulating plate 11. The extent of rotation is limited by the extent ofslits 14 in the plastic ring 10. The lower side of the insulating plate11 has a metallic ring 15 secured thereto which is formed at variouspoints of its circumference with pinching or friction holding springs 16to secure the third part of the sensor thereto. On those points wherethe insulating plate 11 engages with inwardly extending angles 4,metallic ring 15 is formed into projections 17 which extend to the upperside of insulating plate 11. If, for example, due to excessive heating,for example due to a fire, insulating plate 11 deforms, metallic ring 15will still secure the sensing element together by catching on, andbearing against the angles 4 of the socket part.

The upper side of insulating plate 11 has a metallic hood 18 securedthereto, defining therein a reference ionization chamber. Hood 18 hasone or more cam projections 19 which fit into slits 20 of part 5 andprovide a guide for the proper fitting together of the first and secondportion of the sensor. A doubled electrode 21 is located centrally ofthe plastic ring 10. Double electrode 21 is formed with double-sided endfaces, like a double mushroom, and radioactive substances 22, 23 arelocated at the flat faces of the double-sided electrode 21. The variouscomponents of the electrical circuit 24 are located in the space betweenring 10 and insulating plate 11. The connecting wires are connected toappropriate points of the printed circuit on the upper side of theinsulating plate 11. The embodiment illustrated utilizes two ionizationchambers, connected to a field effect transistor (FET) having highlyinsulated input. in order to improve isolation between the adjacentconnecting wires, the field effect transistor is encapsulated within asuitable insulating mass, and located in the space between plate 10 andplate 11. A control lamp 26, visible from the outside, indicates thestate of sensing of the ionization sensor.

The third portion of the sensor comprises a metallic shroud 27, havingopenings 28, 29 for surrounding atmosphere. The upper edge 30 of shroud2 7 is bent over outwardly, so that, upon attaching together the secondand the third portion, it will catch over holding springs 16. Removal ofthis interengagement is possible only when springs 16 are pressedoutwardly, so that shroud 27 can be removed.

A labyrinth 31, made of highly insulating plastic material, is locatedin the interior of shroud 27. it includes a series of annularprojections 32 to increase the surface leakage path, that is the creepdistance between the housing of the shroud and the inner electrode.Opening 33 is formed in the interior of the labyrinth 31 to permit themushroom end of electrode 21 to pass therethrough. Labyrinth 31 issecurely pressed to annular projections 34 formed on the plastic ring10, when the sensor is assembled together. Thus, the surface leakagepath between the center electrode 21 and the shroud 27, forming thecounter electrode, is increased by at least four times the minimumdistance. Additionally, the surface of plastic ring 10 is sealed by thepresence of labyrinth 31, so that smoke and dust will precipitate inthose portions of the measuring chamber which form part of the thirdelement of the fire alarm sensor. The sensor can thus be effectivelycleaned by mere removal of the third part without removing the sensitiveportions of the electrical circuit or the radioactive substancestherein. This completely prevents damage of the fire alarm sensor duringmaintenance, and any danger to personnel during cleaning or repair.

The second portion may, additionally, be secured against undesired andunauthorized removal by means of a set screw 35 located in ring whichpresses the insulating plate ii to angle 4 to such an extent that angle4 can no longer pass over cam 13. The third portion, that is the thirdelement of the sensor, can be removed without difficulty, whereas thesecond portion can be removed only by additional loosening of the safetyset screw.

The upper side of the labyrinth 31 is formed with an annular projection6 which, when the parts are assembled together, fits into acorresponding groove 37 of ring lit). This presses pin 38 upwardly, thusopening a short circuit switch. Field effect transistor 25 is thusprotected from damage by accidental contact of the electrodes whenshroud 27 is removed (see Swiss Pat. No. 460,594 for a full disclosure,which is hereby incorporated by reference). it necessary, shroud 27 mayhave a second shroud 39 applied'thereover (see Swiss Pat. No. 475,614,hereby incorporated by reference) which has atmospheric inlet openings40 offset with respect to openings 28, 29 of shroud 27. Thissubstantially decreases the sensitivity of the ionization fire alarmsensor to air currents.

FIG. 2 additionally shows a suitable removal tool, adapted for theremoval of the components of the sensor of the present invention. Itessentially comprises a cylindrical shell 41 which fits exactly in thespace between shroud 27 and ring 10. Placing shell 41 in this spacecompresses springs 16, by pressing them radially 30 outwardly,-thusremoving the third element of the sensor from the second and permittingits longitudinal removal. If, additionally, the element is rotated, thenangles 4 will slip over the cams 13 (provided set screw is loosened, orabsent) to enter slits 12, and the second part of the sensor can beremoved from socket l together with shroud 27 This shell can readily besecured to a long pole so that portions of the sensor can be replaced orcleaned from the floor surface without requiring that personnel carryand mount ladders. This substantially decreases the period of time persensor for maintenance. Simple and fast cleaning of the sensing elementis thus possible without danger that potentially hazardous, or delicateparts of the sensor might be touched. Maintenance c'an'thus be entrustedto less than highly skilled personnel.

The arrangement in accordance with the present invention is so madethat, if the sensor is subjected to a temperature high enough that allplastic parts therein will melt, constructional integrity of the sensoritself is not impaired. All three portions of the sensor will notseparate and particularly the radioactive substance will not fall out ofthe sensor but remain therein. This effectively inhibits radioactivecontamination of the location of a tire.

Various equivalent constructions can be used, and the present inventionis not limited to the specific arrangement of parts described in detail.The essential feature is to form the sensor of single parts so that oneelement, that is one component includes all the sensitive andpotentially hazardous parts, another one provides a shield or shroudprotecting the sensitive and potentially hazardous parts against dust,dirt or other contamination and the third secures the assembly to asupport, such as a ceiling; whereas all parts are so constructed thatthey are independently separable and connected by independently operableinterlocking arrangements. The specific type and arrangement of theinterlocks themselves can be selected depending on the specific form andshape of the sensing elements.

The third part ,of the sensor which is particularly subject to dirt anddust is so constructed that all sensitive elements of the second part,and particularly the insulation path; between the electrodes of theionization chamber are so covered, when the third part is attached tothe second, thatcontamination by deposit of dust, or the like, isavoided.

We claim:

1. Ionizing-type fire alarm sensor comprising a housing structure havingat least three interlocked parts formed with engaging, self-locking,independently separate interlock means to hold the three parts togetherand permit individual separation of the parts from each other;

a first part forminga socket adapted to be secured to a support andbeing formed with electrical contacts and adapted for connection to afire alarm system;

a second part comprising separable contacts engaging the contacts ofsaid first part, means defining one position of an ionization chamber,radioactive ionizing substances being located on the second part andcomprising all radioactive substances of the sensor, part of theionizing substance being located in said chamber, and an electricalcircuit means responsive to changes in electrical characteristics of theatmosphere in the chamber;

and a third part separable from said second part independent ofseparation or nonseparation of the second and first parts, said thirdpart comprising the other non-radioactive portion of the ionizationchamber and including shield elements fitting against the second part toform a dust and dirt shield for the second part when the second andthird part are connected together.

2. Sensor according to claim 1, wherein the interlock means comprisesspring elements secured to at least one engaging part and having anovercenter position to positively seat and position the engaging parts.

3. Sensor according to claim 1, wherein the interlock means between thefirst pair of adjacent parts are separable. upon motion in apredetermined direction;

and the interlock means formed between one of the parts of the firstpair and the remaining part are separable upon motion in a differentdirection.

4. Sensor according to claim 3, including separable removal meansindividually engageable with at least one of said parts, said one partbeing formed with means engageable with said removal means;

said removal means being adapted for transferring removal motion inbothrotary and longitudinal direction.

5. Sensor according to claim 1, wherein the interlock means between afirst pair of adjacent parts are separable upon rotary motion and theinterlock means formed between one of the parts of the first pair andthe remaining parts are separable upon longitudinal motion.

6. Sensor according to claim 5, wherein the interlock meansinterconnecting the first pair comprises a bayonet-type interlockrequiring both rotary and longitudinal movement, the longitudinalmovement being spring-loaded.

7. Sensor according to claim 1, wherein the interlock means comprisesmetallic interengaging elements remaining engaged even upon melting ofnon-metallic elements of the sensor.

8. Sensor according to claim 1, wherein the second part comprises anelectrode terminal connected to the electrical circuit means;

and wherein the third part comprises a metallic housing and the shieldelements include an insulating labyrinth separating said electrodeterminal from said metallic housing, said labyrinth being shaped toextend the surface creep path between the electrode terminal and thehousing by at least four times the minimum distance therebetween.

9. Sensor according to claim 1, wherein the second part includes aninsulating plate;

and the electrical circuit means comprises a printed circuit on saidinsulating plate.

ber.

1. Ionizing-type fire alarm sensor comprising a housing structure havingat least three interlocked parts formed with engaging, self-locking,independently separate interlock means to hold the three parts togetherand permit individual separation of the parts from each other; a firstpart forming a socket adapted to be secured to a support and beingformed with electrical contacts and adapted for connection to a firealarm system; a second part comprising separable contacts engaging thecontacts of said first part, means defining one position of anionization chamber, radioacTive ionizing substances being located on thesecond part and comprising all radioactive substances of the sensor,part of the ionizing substance being located in said chamber, and anelectrical circuit means responsive to changes in electricalcharacteristics of the atmosphere in the chamber; and a third partseparable from said second part independent of separation ornonseparation of the second and first parts, said third part comprisingthe other non-radioactive portion of the ionization chamber andincluding shield elements fitting against the second part to form a dustand dirt shield for the second part when the second and third part areconnected together.
 2. Sensor according to claim 1, wherein theinterlock means comprises spring elements secured to at least oneengaging part and having an overcenter position to positively seat andposition the engaging parts.
 3. Sensor according to claim 1, wherein theinterlock means between the first pair of adjacent parts are separableupon motion in a predetermined direction; and the interlock means formedbetween one of the parts of the first pair and the remaining part areseparable upon motion in a different direction.
 4. Sensor according toclaim 3, including separable removal means individually engageable withat least one of said parts, said one part being formed with meansengageable with said removal means; said removal means being adapted fortransferring removal motion in both rotary and longitudinal direction.5. Sensor according to claim 1, wherein the interlock means between afirst pair of adjacent parts are separable upon rotary motion and theinterlock means formed between one of the parts of the first pair andthe remaining parts are separable upon longitudinal motion.
 6. Sensoraccording to claim 5, wherein the interlock means interconnecting thefirst pair comprises a bayonet-type interlock requiring both rotary andlongitudinal movement, the longitudinal movement being spring-loaded. 7.Sensor according to claim 1, wherein the interlock means comprisesmetallic interengaging elements remaining engaged even upon melting ofnon-metallic elements of the sensor.
 8. Sensor according to claim 1,wherein the second part comprises an electrode terminal connected to theelectrical circuit means; and wherein the third part comprises ametallic housing and the shield elements include an insulating labyrinthseparating said electrode terminal from said metallic housing, saidlabyrinth being shaped to extend the surface creep path between theelectrode terminal and the housing by at least four times the minimumdistance therebetween.
 9. Sensor according to claim 1, wherein thesecond part includes an insulating plate; and the electrical circuitmeans comprises a printed circuit on said insulating plate.
 10. Sensoraccording to claim 1, wherein the electric circuit means includes afield effect transistor located on said second part and beingencapsulated in an insulating mass.
 11. Sensor according to claim 1,including additional locking means securing the first and second partstogether and permitting separation of the first and second part onlyupon disengagement of said additional locking means.
 12. Sensoraccording to claim 11, wherein the additional locking means comprises aset screw.
 13. Sensor according to claim 1, wherein the second partincludes a second or reference ionization chamber.